In Goble et al. U.S. Pat. No. 5,417,692 a bone fixation and fusion system is disclosed, for example for the fusing of toe bones or the like together by firmly locking them in abutting relation to permit good healing. This is accomplished through the use of a male and female connector which, when bone fusion is the desired result, each have external bone threads so that each of the connectors may be driven into a separate bone.
The male connector is a solid, threaded body having a cross cut cylindrical sleeve with a split ring on the distal end. The female connector defines a cylindrical cavity having walls which may define spaced annular grooves or threads. The ring periphery on the distal end of the cylindrical sleeve 15 is intended to engage the grooves or threads in a somewhat resilient, spring-like manner resulting from the cross cut slots, for retention of the two connectors together.
It is of course desired for the two connectors to be retainable together in varying positions, to provide the best possible amount of fit between the bone fixation infusion system of the Goble et al. patent and the respective bones which carry them. In FIG. 9 of the Goble et al. patent the grooves 20b are shown to be provided in spaced relation, but there the spacing may be too wide to provide an optimum fit between the bones, i.e., the bones may be placed too near or too far from each other, because the best fit would be at a position between two of the grooves 20 or 20 b.
In FIG. 10 of Goble et al. xe2x80x9cthreads 21xe2x80x9d are shown which are positioned more closely together than the grooves of FIG. 9. However, if the xe2x80x9cthreadsxe2x80x9d are true screw threads, then they are of helical shape, so that anything that would fit within the threads must be slightly angled away from perpendicular to the axis of the connectors. Accordingly, the split ring 18, 18a formed around the distal end of the cylindrical sleeve 15 described above will not fit well within helical threads, with the result that the retention of the two connectors may be more easily broken, and the connectors may separate in an undesirable, unplanned manner.
If the xe2x80x9cthreads 21xe2x80x9d of Goble et al. are parallel, machined, annular grooves like the grooves 20b of FIG. 9, these are difficult to machine, particularly finely cut, closely spaced annular grooves of the size illustrated in FIG. 10, making the manufacture of the connector system of Goble et al. difficult.
By this invention, an improvement is provided in which a screw thread may be provided to both of the connectors, to be engaged in a well-fitting, solid connection which nevertheless is highly adjustable in its length. The screw threads which are used in this invention are easily machineable, to provide a lower cost, more reliable connection between the connectors of the bone connector system of this invention.
By this invention, a bone connector system is provided which comprises first and second connector members. At least one of the connector members carries an external bone screw thread to permit securance within a bone. In the circumstance where two bones are being connected together for fusing or the like, both of the connectors may carry external bone screw threads, to permit their separate securance within separate bones. Otherwise, one of the connector members may connect to an artificial tooth or another attachment to a bone.
One of the connector members defines a projection or boss having an outer end. Longitudinal slots extend through portions of the boss adjacent the outer end. The boss also carries a plurality of loops of an external screw thread adjacent to the outer end.
The other of the connector members define a bore for receiving the boss, having a multiple-loop, internal screw thread which is proportioned to engage the external thread of the boss when the connectors are brought together. Preferably, the multiple-loop internal thread has more loops than the external screw thread, so that the loops of the external screw threads can slide longitudinally along an array of loops of internal screw thread, and the respective threads may engage each other at a continuum of positions, so that the length of the bone connector comprising attached first and second connector members may be adjusted to the most desired fit along a series of very closely spaced, stepwise positions. The internal screw thread and the external screw thread may fit together with a multiple loop, close, tight fit without any mispositioning, as can be provided by a ring 18 as Gobel et al in extending perpendicular to the axis of the connector members when the ring is attempting to engage with a thread within the bore.
If desired, one or both connector members may define a central lumen, to permit a guidewire to extend through either or both connector members to facilitate placement thereof at a desired position in a bone. For example the connector member which does not define the boss may define a central lumen extending completely therethrough, being useable with the connector member having a boss and, with or without such a lumen.